It is known to provide a linear actuator such as a hydraulic cylinder between a vehicle body end of a lateral link or a trailing arm of a wheel suspension unit for supporting each rear wheel and the vehicle body, and to individually control the toe angles of the right and left wheels by extending or retracting the corresponding linear actuators (see Japanese patent publication No. 8-25482 and Japanese patent laid open publication No. 9-30438).
In conventional variable rear wheel toe angle control systems including those disclosed in these patent publications, it was customary to base the design on a simple rear wheel steering system. The toe angle of the rear wheels was controlled according to the behavior of the vehicle as it turns, and the control target value of the rear wheel toe angle was determined in dependence on the front wheel steering angle, lateral acceleration and/or yaw rate.
In such a system, the lateral acceleration and yaw rate are produced as a result of a change in the heading direction of the vehicle. Therefore, a response delay was inevitable because the control value of the toe angle is based on the lateral acceleration and yaw rate. Also, if the rear wheel toe angle is changed in response to a steering action of the front wheels, the stability of the vehicle in traveling along a straight path may be impaired because such a steering action may have been taken as an effort to maintain the straight course of the vehicle when the vehicle is subjected to a cross wind or when the vehicle is traveling over an irregular road surface.